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Rise in snake fungal disease draws researchers’ attention

Posted July 1, 2013

Wildlife officials are monitoring a fungal disease infecting certain wild snake populations in the Eastern and Midwestern United States.

Fungal infections were occasionally reported in free-ranging snakes prior to 2006. But the U.S. Geological Survey’s National Wildlife Health Center has recently seen a spike in the number of snakes with fungal dermatitis submitted to the center and other diagnostic laboratories.

Laboratory analyses show that the fungus Ophidiomycesophiodiicola is consistently associated with snake fungal disease, but additional fungi are often isolated from affected snakes. To date, there is no definitive evidence that O ophiodiicola causes SFD.

The most consistent clinical signs of SFD include scabs or crusty scales, subcutaneous nodules, premature separation of the outermost layer of the skin from the underlying skin, white opaque cloudiness of the eyes not associated with molting, or localized thickening or crusting of the skin. Skin ulcers, swelling of the face, and nodules in the deeper tissues of the head have also been documented.

Clinical signs of SFD and disease severity may vary by snake species. Aside from the presence of fungi with disease-associated lesions, specific pathological criteria for the disease have not yet been established.

While death has been associated with some cases of SFD, population-level impacts of the disease are not yet widely known and are difficult to assess because of the cryptic and solitary nature of snakes and a general lack of long-term monitoring data.

In New Hampshire, clinical signs consistent with SFD were associated with a 50 percent decline in an imperiled population of timber rattlesnakes from 2006-2007. In areas where susceptible snake species live in small, isolated populations, the added threat of SFD may threaten viability of these populations. SFD has been observed in other regions without suspected or documented population declines.

The wildlife health center has confirmed fungal dermatitis in wild snakes in Florida, Illinois, Massachusetts, Minnesota, New Jersey, New York, Ohio, Tennessee, and Wisconsin. However, SFD is suspected to be more widespread in the United States than is currently documented.

Multiple snake species have developed SFD, including the northern water snake, rat snake, and timber rattlesnake.

Jeff Lorch, PhD, is a research associate at the University of Wisconsin-Madison studying SFD at the wildlife health center. “The top research priority right now, aside from determining what the causative agent is, is to answer that question of whether this is something that’s going to be a problem for all snake populations,” Dr. Lorch said.

“We also want to determine what happens when snakes are infected with Ophidiomyces,” he said. “Do they all die, do some recover? Maybe the fungus isn’t a widespread threat, but it could endanger small isolated populations of snakes by making their recovery more difficult.”

Several agencies, organizations, researchers, and other key stakeholders, including the National Wildlife Health Center, are working together to investigate this potentially emerging disease and to learn what impacts SFD is having on wild snake populations.